Electromagnetic switch.



J. l. WOOD.

ELECTROMAGNETIC SWITCH.

APPLICATION FILED NOV. 20. 1914.

Patented Aug. 13, 1918.

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1.1. WOOD.

ELECTROMAGNETIC SWITCH.

APPLICATION FILED NOV. 20. 1914.

' Patented Aug. 13, 1918.

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H15 ATTORNEY.

f TED STATES PATENT ornron.

JAMES J. woon, orron'r WAY E, INDIANA, ASSIGNOR TO, GENERAL ELECTRICCOMPANY, .A CORPORATION on NEW YORK.

ELECTROMAGNETIC SWITCH.

'Speqificationof Letters Patent.

Patented; Aug. 13, 1918,

Application filed November 20, 1914. Serial No. 873,212.

To all whom it concern:

Be it known that I, James J. WOOD, a citizen of the United States,residing at Fort Kayne, county of Allen, State of Indiana, have inventedcertain new and useful Imp cm n sin ec oma n Sw t h of whichthejfollowing is a specification.

This invention relates to electromagnetic switches for the. control, ofelectric circuits and has forits object the. provision of improved meanswhereby an electric circuit may be controlled in a reliable, simple andeffi ient manner. f i

My invention relates more specifically to electromagnetic switches forcontrolling electric motor circuits, one of the objects being to providea device of this character which will efi'ect the automatic starting ofthe motor under the control of the motor current. In the operation ofelectric motors it is common to" both start the motor and control itsspeed. by means of a resistance which is cut in and out of circuit.Every time a section of resistance is cut out the current temporarilyrises above normal value. The increase in speed which is caused by thecutting'out of the section of resistance immediately reduces thecurrent. During the starting of the motor, therefore, there is, atemporary rush of current for each section of resistance which is cutout. These sections are frequently cut out of circuit by electromagneticswitches which operate auitomaticall'y in succession. In order toprevent the switche's from operatingtoo rapidly and. increasing thecurrent beyond 'a safe value,variousmeans have been devised. Ail idealswitch forthispurpose is one containing a winding which'carries themotor current and a switch member controlled thereby for cutting out theresistance, the arrangement being such that the switch member-win not beoperated to cut out the resistance until the current has fallen to. apredetermined value and-twill assnme an open position when the. windingis deenergiz'ed.) A switch of this character was invented by Walter O.Lum and forms the subject matter of an application, Serial, No. 611,151,filed February 27, 1911, assigned to the same assignce as thisapplication.

lVhile the broad features of my device aredescribed and claimed in the,said Lum application, the morejspecific features thereof constituteimportant improvements which lend themselves to eiiiciency of operationand also make the device more accurate and positive in operation.Likewise, the improved mechanical construction of the switch renders itmore rugged and comact and likewise decreases th'e cost of production.

In the accompanying drawings illustrating one form of my invention,Figure 1 is a side elevation. of a. complete electromagnetic switchembodying my improvements; Fig. 2 is a front elevation of the same; andFigs. 3, 4.- and' 5 show in outline the variouspositions which theswitch assumes; and Figs. 6 to 10 are similar views of a modified formof my invention.

Referring first to Figs. 1 and 2, 10 represents an energizing windingfor magnetizing the magnetic structure composed of a core 11 j oined. atits inner end to a U-shaped magnet frame 12, the ends of which formpoleifaces l3 and 14. These parts constituting an electromagnet aresecured to an insulating base 15 and. a stationary contact16 is suitablysupported above the electromagnot so as to cocperate with the movablecontact in a manner hereinafter described. Supported by lugs 17projecting from the end of the magnet is a switch member 18 of magneticmaterial. The lugs 17 are on a bracket, preferably of brass, which issecured to the end of the core by being fitted over its reduced end.This switch member is pivoted intermediate its ends in the lugs 17 soasto cooperate with the two polepieces 13 and 151. T o the upper end ofthe switch member is pivoted the contact 19 and a spring 20 isinterposed between the member and the contact support so as to give ayielding pressure between contacts 16 and 1 9, which are shaped so as toclose with a wiping or rolling action. Pivoted on the same pivot 17as'that of the switch member is a pressure element 21 of magneticmaterial arranged to cooperate with the polepiece 14 and be attractedthereby when the winding is energized. The end of this element isturnedto form a lip 21' to improve the magnetic circuit at that point.The purpose of this element is to place a spring pressure upon theswitch member to give it a tendency to close while the switch member isbeing held in the open position by the polepiece 13. The particular formof this switch member and of the pressure element 21 form no part of mypresent invention, but for purposes of illustration I have shown theupper part of the switch member as being composed of two curved armsunited at their outer ends by a strut 22.. The pressure'ele ment 21 fitsin between these two arms and has two wing portions which are as wide asthe arms so as to make the maximum width the same as that of the switchmember, and are curved to conform to the shape "of the arms. The outerends of these arms cooperate with the pole face 14, which is providedwith projections 14 to give a pole area at these points equal to that ofthe ends of the arm, and the pressure element locatedbetween these twoends also cooperates with the main portion of the polepiece. A tensiondevice is interposed between the pressure element 21 and the switchmember 18. This consists of a spring'24 having a bearing upon the switchmember, which spring is compressed by means of a rod which is pivoted inthe pressure element and extends between the two arms of the switchmember.

The spring 24 surrounds the rod 25 and a nut 26 is screwed on the endofthe rod to act as a stop bearing for the outer end of the spring. Whenthe pressure element is pulled in and the switch member is held out bythe magnetic pull at the pole piece 13 due to a high current (see Fig.4) the spring will be compressed a certain amount. When the switchmember follows the pressure element in response to the spring pressurewhich overcomes the decreased pull of the pole piece due to a lowermagnetizing current (see Fig. 5) the spring would be relaxed bysubstantially the amount which it has been compressed, and the effectivepressure on the contacts will not be as great as would be desirable. Inorder to overcome this disadvantage and offset the effect of therelaxation of the spring, the tension device is arranged so as toincrease its eifect upon the switch member by increasing its effectiveleverage upon the member as the latter moves inward to closed position.To this end, the inner end of the spring is mounted upon a washer 27which is pivoted between the two arms of the switch member on a pin 28so as to have the effect of a rocker bearing. As shown in the drawing,(Figs. 4 and 5) it will be obvious that as the switch member movesinward in response to the pressure of the-spring 24 supplemented by thepull at the pole face 14, the rod 25 will 7 be rocked slightly outwardaround its pivot toward a position perpendicular to the pressure member,that is, the center of the spring will move toward substantially aposition of maximum effect. As shown in Fig. 5, the

spring has moved substantially to this maximum position. 7 Thisincreases the pressure between the contacts over what it would be if theline of action of the spring did not stantially up to what it would beif the 7 spring had not been relaxed by the inward movement of theswitch member, which condition would exist if the switch member werereleased, but instead of moving toward the stationary member, thestationary Qmember would move toward it. By adjusting the screw 26 thepressure on the spring and consequently the value of current at whichthe switch will close will be adjusted.

V In the operation of my device, when the. winding 10 is energized abovea predetermined value, the flux across the gap at the pole facelS willhold the switch member in open position; At the sametime the member 23will bedrawn inward and the spring compressed. The parts will now beinthe position shown in Fig. 4. There will nowbe two forces controllingthe switch, one due to the pressure of the spring and the other, whichmay be negligible, due to the pull of the polepiece 14. Opposed to theseclosing forces is the holding out force due to. the magnetic pull of thepolepiece 13. The switch will therefore remain in open position untilthe'current has fallen to the predetermined value. As the currentdecreases the magnetic flux at the polepieces 13 and 14 will bedecreased, and hence both the clos- 111g magnetic force and the holdingout magnetic force will be decreased. The closing closed, position, theholding out gap is greatly increased and the closing gapdecreased, sothat the magnetic pulltoward closing position increases rapidly untilthe switcharm comes in contact with the polepiece 14 and is pulledstrongly so as to press the contacts firmly together. As the switchmember moves inward toward closed position, the arm 25 moves outwardtoward the tangential or position of maximum effort. This increases theleverage of the spring upon the switch member and offsets to a largedegree the effect of the decreased tension on-the'spring. The contactswill therefore be held together .with a maximum' spring pressure. Byadjusting the screw 26 the value of current at which the switch closesmay be adjusted, the screw 26 may be left stationary and the adjustmentbe made by ad usting the 'air gap at the polepiece 13 by turningthe'screw 29. V r

In FigsQG to 10 I have shown a modified" form of my invention, in whichtwo windings are employed instead of one. I have shown these windings asbeing in series with each other so that the current between the twowindings will decrease proportionately although, of course, thisparticular arrangement of winding is not an essential feature of myinvention. By referring to Figs. 6 and 7 it will be seen that the twowindings and 31 are mounted respectively on cores 32 and 33 which areconnected together at their inner end by a plate of magnetic material34. Supported between the two windings is a standard 35 of magneticmaterial, which is connected with the plate 34, and forms a pivotalsupport for the movable parts. The switch member 36 which in this caseis substantially the same in shape as that shown in Fig. 5, is pivotedat 37 and its lower end 38 is provided with an adjusting screw 39. Anauxiliary pole piece 40 is secured to the upper core and bent outward,as shown, to coiiperate with the end of the switch member. The member 41pivoted concentrically with the switch member, opcrates between theauxiliary polepiece 40 and the switch member. The tension device betweenthe pressure element and the switch member is the same as that shown inFig. 5, and further description is therefore unnec essary. One advantageof a construction of this character is that it is possible toconcentrate the flux so as to apply a greater holding out force becauseof the presence of the coil 31. On the other hand, it has thedisadvantage of having an extra coil and not being so rugged andcompact.

The operation of this form of my device is substantially the same asthat described with reference to Figs. 1 to 5, the difi'erence in theacting forces being chiefly one of degree. Figs. 8 to 10 show the partsin the various conditions, and correspond to Figs. 3, f and 5.

While I have described my invention in concrete form and as operating ina specific manner in accordance with the patent statutes, it should beunderstood that I do not limit my invention thereto as variousmodifications thereof will suggest themselves to those skilled in theart without de parting from the spirit of my invention, the scope ofwhich is set forth in the annexed claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is

1. An electromagnetic switch comprising an electromagnet, a movableswitch member normally in open position, an element movable by saidmagnet, and a tension device interposed between said element and saidswitch member to force them together,

said device comprising a spring having a rocker bearing upon the switchmember causing the spring to shift as the member moves under theinfluence of the spring and increase the leverage at which it acts uponthe switch member to close it, and means for holding the member againstsaid closing tendency when the magnet is energized above a predeterminedvalue.

2. An electromagnetic switch comprising an electromagnet, a switchnormally in open position, an element movable by said magnet, a tensiondevice interposed between said element and said switch comprising a rodprovided with a stop pivoted to the element, and extending through theswitch member, a spring surrounding said rod between the stop and theswitch member, and having a rocker bearing upon the latter, and meansfor holding the member in open position against the tension of thespring when the magnet is energized by a current above a predeterminedvalue.

3. An electromagnetic switch comprising an electromagnet having twopolepieces, a switch member cotiperating with said pole pieces andpivoted between them, an element pivoted concentrically with said switchmember and movable into contact with one of said pole pieces when thewinding is energized, a rod provided with a stop pivoted to said elementand extending through the switch member, a spring surrounding the saidrod between the stop and the switch member and having a rocker bearingupon the latter, said switch member being held by the opposite polepieceagainst the tension of the spring when the magnet is energized by acurrent above a predetermined value.

4. An electromagnetic switch comprising an electromagnet, a movableswitch member normally in open position, an element movable by saidmagnet, a spring interposed between said element and said switch memberto give the latter a tendency to close when the magnet is energized,means whereby the spring is caused to act upon the switch member as itcloses so as to increase the leverage,

means for holding the member in open position against said closingtendency when the magnet is energized by a current above a predeterminedvalue, and a pole piece for pulling the member into closed position whenreleased.

In witness whereof, I have hereunto set my hand this 14th day ofNovember 191%. JAMES J. WVOOD. Witnesses:

N. E. CRANE, L. M. GURMAN.

Copies of this patent may be obtained for five cents each, by addressingthe Commissioner of Patents,

Washington, D. G.

